Raman scattering of the model multiferroic oxide BiFeO3: effect of temperature, pressure and stress

International audience; The perovskite Bismuth ferrite BiFeO3 (BFO) is considered to be a model multiferroic and offers a rare multiferroelectric robustness since it presents a coexistence of ferroelectric and antiferromagnetic order up to unusually high temperatures. Perovskite-type materials are known for their common structural instabilities which can be driven by diverse external parameters like temperature, pressure, stress etc. Such instabilities and the associated structural distortions are often very subtle and difficult to detect by techniques probing the average structure such as X-ray diffraction. Here we present an investigation of the BFO phonon spectrum by the local probe Raman spectroscopy as a function of polarization, temperature and pressure. We review a recent temperature-dependent Raman investigation which illustrates a first-order structural phase transition at the ferroelectric Curie temperature. Our temperature dependence results further indicate a phonon-anomaly around the magnetic Néel temperature, which is discussed in the light of multiferroicity. We will further illustrate that BFO presents important pressure-induced structural instabilities and we discuss the role of such instabilities for the understanding of strained thin film BFO which show distinct properties compared to the bulk.